1. Technical Field
This disclosure relates to a serial interface interposed between two serially connected unit cells, thereby forming a connection mechanically and conductively coupling the unit cells.
2. Discussion of Related Art
In general, alkali storage batteries—such as nickel-hydride storage batteries, nickel-cadmium storage batteries, etc., or lithium-based storage batteries such as lithium-ion cells, lithium-polymer cells, etc.—are generally manufactured by interposing separators between cathodes and anodes, then helically winding them; coupling current collectors to the ends of the cathodes and the anodes to form electrodes, disposing the electrodes within metallic outer cases, welding lead portions extending from the current collectors to seals; and mounting the seals on openings of the outer cases while interposing insulating gaskets therebetween. Because such an alkali storage battery requires a high output when used, for example, as a power source for an electric motor or an electric automobile, etc., alkali storage batteries have generally been assembled into a module cells made by connecting a plurality of individual cells in series. Where storage batteries are used in high output applications such as powering a large electric motor or an electric automobile, the module cell comprising a plurality of cylindrical unit cells coupled in serial and/or parallel have been used.
FIG. 1 shows in perspective, a plane-frame module cell 10 comprising a parallel arrangement of cylindrical serial cells 30 in a frame 20, the cylindrical serial cells 30 being formed by serially connecting a predetermined number of cylindrical unit cells 40. Although only a lower frame receiving the cylindrical serial cells 30 is shown in the FIG. 1, there may also be one or more upper frames having a structure similar to that of the lower frame stacked thereon.
In the cylindrical serial cells 30 shown, a serial interface is interposed between the two serial unit cells 40, the serial interface mechanically securing and electrically coupling the two unit cells.
Lithium-ion unit cells do not normally outgas. Internal and/or external conditions can cause physical and/or chemical problems that increase the internal pressure of a cell, however, which can rupture a safety vent of the cell. Consequently, a structure (Degassing structure) for discharging a high pressure gas generated in the cell to the outside environment is required in order to mitigate this pressure.
In nickel-metal-hychoride (Ni-MH) cells, gases are normally generated by internal chemical reactions and discharged out of the cell. This gas is continuously discharged, and does not typically cause a problem if vented to the outside environment. However, where the unit cell is sealed, for example, by a serial interface, gas can accumulate over time adversely affecting the unit cell and/or risking explosion.
Accordingly, there is a need for a serial interface providing sufficient mechanical strength to serially connect two cylindrical unit cells and to conductively connecting the unit cells, as well as to permit discharge of high pressure and waste gases.